In modern surgery one of the most important instruments available to medical personnel is the powered surgical tool. Typically this tool comprises a drill unit in which a motor is housed. Secured to the drill unit is a cutting attachment that is designed to be applied to a surgical site on a patient in order to perform a specific medical procedure. For example, some powered surgical tools are provided with drills or burrs for cutting bores into hard tissue or for selectively removing hard tissue. Still other powered surgical tools are provided with saw heads. These tools are used for separating large sections of hard and soft tissue. The ability to use powered surgical tools on a patient has lessened the physical strain of physicians and other personnel when performing medical procedures on a patient. Moreover, most surgical procedures can be performed more quickly and more accurately with powered surgical tools than with the manual equivalents that proceeded them.
One type of powered surgical tool that is especially popular with some physicians is the cordless, battery operated powered surgical tool. As the name implies, this type of tool is provided with a battery that serves as the power source for the motor. This eliminates the need to provide the tool with a power cord that is connected to an external power source. Like many other powered surgical tools, a typical cordless, battery operated surgical tool has a handgrip similar to a pistol handgrip. The tool motor is contained within a housing located on top of and integral with the handgrip. The motor is typically actuated by an ON/OFF switch that extends forward from the front surface of the handgrip. The ON/OFF switch, in addition to controlling the ON/OFF state of the motor, also controls the energization current supplied to the motor so as to control the speed of the motor. The electronics that control the motor are typically located in the housing adjacent the motor. In a cordless surgical tool, the battery that supplies the energization current for the motor is typically housed in the handgrip.
The elimination of the power cord offers several benefits over corded, powered surgical tools. Surgical personnel using this type of tool do not have to concern themselves with either sterilizing a cord so that it can be brought into the sterile surgical field or ensuring that, during the medical procedure, an unsterilized cord is not inadvertently introduced into the surgical field. Moreover, the elimination of the cord results in the like elimination of the physical clutter and field-of-view blockage a cord otherwise brings to a surgical procedure.
While cordless surgical tools in many situations offer considerable improvements over their predecessors, they are not without some disadvantages. Many cordless powered surgical tools are provided with electro-mechanical ON/OFF switches. The ON/OFF switch, as well as the rest of the tool, is often placed in an extremely harsh environment in order to sterilize the tool. For example, it is not uncommon to sterilize a powered surgical tool by placing it in a chamber where the temperature is approximately 270.degree. F., the humidity is at or near 100% and the atmospheric pressure is approximately 30 psi. The repeated exposure of the mechanical contact points of the ON/OFF switches employed in many surgical tools to this type environment causes the components of these switches to corrode. This corrosion, in turn, causes these switches to malfunction. As a result it has become necessary to replace the ON/OFF switches of some power tools at an expensively high frequency.
Moreover, when providing a powered surgical tool, it is desirable to design the tool so that the motor and associated cutting attachment can be rotated in first, forward direction and in a second, reverse direction. This minimal control over the direction of motor rotation makes it possible to drive a cutting attachment such as a drill in both forward and reverse directions so that the attachment can easily be forced into and removed from the surgical site.
It has also become increasingly desirable to design powered surgical tools, including cordless powered surgical tools, so that they oscillate the complementary cutting attachments between the forward and reverse rotations. It is, for example, desirable to drive a drill bit in an oscillatory rotational pattern when the bit is initially applied against bone; so driving the bit has been found to reduce the tendency of the bit to skew prior to the bore hole forming. It has also been found desirable to drive a drill bit in an oscillatory rotational pattern when it is used to cut through the opposed side of a bone. Driving a drill bit in this motion minimizes the extent to which soft tissue adjacent to the bone wraps around the bit as the bit exits the bone.
Problems have, however, arisen in providing some powered surgical tools, especially cordless powered surgical tools, with the ability to actuate the motors integral with these tools so that they undergo an oscillatory. rotation. In some tools, especially those like cordless tools wherein the motor is housed in a part of the tool separate from that handgrip held by the surgeon, the oscillatory motion has been found to vibrate the tool to such an extent that a surgeon cannot firmly hold it. This movement is sometimes referred to as tool "bucking". Moreover, a considerable amount of the power applied to these motors when they oscillate is apparently converted into heat instead of being used to actuate the associated cutting attachments. Over time, this heat, which is simply absorbed by the motors, can cause the motors themselves to wear out at a relatively high rate. A further undesirable side effect of this heating when it occurs in a cordless powered surgical tool is that it means energy from the battery that should be used solely to drive the cutting attachment is lost to needless tool heating.
Still another disadvantage of many powered surgical tools, including battery powered surgical tools, is that it has proved difficult to provide switches that allow the surgeon using the tool to easily control both the direction in which the tool motor turns (forward, reverse, or oscillatory) and the speed of the tool. Many powered surgical tools are designed so that the forefinger switch, (the trigger finger switch), located on the leading surface of the handgrip only controls the ON/OFF state of the motor and the motor speed. A second switch typically located along a rear surface of the tool is used to control motor rotation: forward; reverse; or oscillatory. A disadvantage of these tools is that each time the surgeon wants to change motor rotation, he/she must reposition his/her hand holding the tool to actuate the second switch or actuate this second switch with his/her other hand. Either procedure takes time and forces the surgeon to take his/her concentration away from the procedure being performed and, instead, apply it to the tool.